The present invention relates to the operation of cooking appliances having surface burners and particularly such cooking appliances intended for household use as for example in a free standing range or a counter top burner arrangement. Gas ranges, as such appliances are often called, typically have in recent times electrical spark ignitors for the individual burners and employ a manifold connected to the gas supply line with individual user operated manual valves for controlling gas flow to the selected burners. In the design and manufacture of such household gas ranges it is common to have the manifold situated so as to position the control knobs for operating the burner valves on a control console on the front of the range in order that the user need not reach across the burners to operate the controls.
The individual burner valves for household gas ranges commonly have a cam operated switch which closes, upon movement of the valve control to a position for opening the valve, to energize the spark ignitor circuitry. Gas range burner controls of the aforesaid type have been in service for many years and have proven generally reliable and low in manufacturing cost which is an important consideration in mass produced household appliances sold into a highly competitive marketplace.
The aforesaid known gas rangetop burner control arrangements typically have the user actuated control knob for the selected individual burner valve moved to an initial open position in which the cam on the valve shaft closes the switch to energize the spark ignitor; and, subsequently the user moves the control knob to a different position to provide the required gas flow to produce the desired level of flame at the burner and the spark ignitor switch is thereupon opened and the ignitor operation ceases. In the event that the flame is extinguished with the burner valve in the open position, gaseous fuel continues to flow through the burner until such time as the user turns the valve to the closed or "OFF" position. Thus, it has been desired to provide an automatic system for shutting off gas flow to the range in the event of a flame-out condition with the aforesaid type of burner valve-ignitor arrangement.
It is also known in household gas ranges to provide a burner control arrangement for the top burners having a flame sensor with a normally closed switch electrically in series with the ignitor switch on the gas valve. In this latter type system, user manual movement of the burner control valve to any "ON" position causes the cam to keep the ignitor switch closed. The closure of cam operated switch in conjunction with the normally closed flame sensor switch causes the ignitor to continue to operate until the flame opens the flame sensor switch cutting off power to the ignitor. This arrangement has the advantage that in the event of a flame-out the flame sensor switch recloses and activates the ignitor to reignite the gas which continues emanating from the burner; however, the flame sensor adds significantly to the cost of the system.
It has been desired to provide an electrically operated line valve for shutting off gas to the rangetop burner manifold and to the oven burners such that the user can disable the range, such as for prolonged absences or where children will be present and there is a likelihood that the burner valve controls may be tampered with by the children. However, an electrically operated line valve for the purpose of rendering the range inoperative must accommodate the situation where power outages may occur to the household power supply during periods of normal range burner operation and upon restoration of power, prevent a condition where the burner valve would be open and gas caused to flow without re-ignition. Provision must also be made for burner operations during periods when the power is out. Thus, it has been desired to provide a way or means of electrically controlling and disabling a household gas range and in a manner which prevents any undue hazards.